The present invention relates to equipment for use during a downhole drilling operation.
During a downhole drilling operation, in the area of the downhole drilling bit there is usually arranged an electrical sensing member. This electrical sensing member serves to detect the path of the drilling operation. An electrical wireline from a supply at the surface extends along the drilling string and is attached to the electrical sensing member. Typically, the wireline extends along the outside of the drilling string for a certain distance from the drill floor until it reaches a side entry subassembly at which point it enters the interior of the drill string and travels through the drill string until it reaches the sensing member. Such side entry subassemblies are manufactured by Sperry-Sun and are disclosed in U.S. Pat. No. 4,062,551.
The drill string assembly is attached at its upper end to a kelly which passes through a kelly bushing and the opening in the rotary table. As the drill bit advances into the earth, the kelly with the attached drill string moves downwardly with the bit. When the majority of the kelly has entered the hole being drilled, a new drill string member is attached. The drill string and the kelly with the kelly bushing are lifted out of the hole so as to bring the uppermost portion of the top drill string member up through the opening in the rotary table. A plurality of slips are then inserted between the rotary table and the top drill string member so as to secure the top drill string member and the attached drill string assembly to the rotary table. The kelly is then detached from the uppermost drill string member and an additional drill string member is inserted. Typically, one drill string member is inserted at a time. The kelly then is reattached and the drilling operation is continued.
When the top drill string member is secured to the rotary table by the slips, great care must be taken to avoid having any slippage of the slips which can result in damage to the electrical wireline. If the electrical wireline is either pinched or possibly even broken by the slips, the entire wireline must be removed from the drill hole. In order to remove the wireline, the drill string assembly must be removed from the ground until the point of location of the side entry subassembly. This removal takes considerable time away from the productive drilling operations. The wireline then is removed and a new wireline inserted. Such an operation results both in having to discard a significant quantity of electrical wire, which can typically be on the order of 10,000 feet, and a time consuming operation for having to replace the electrical wireline. Such damage, therefore, further increases the cost of the drilling operation.
In addition to preventing damage to the electrical wireline during the steps of adding drill string members, there is a need to prevent the wireline from sliding downward into the drill hole since tension is taken off the wireline during these steps. A clamping mechanism is thus needed and the above-referenced co-pending application shows several embodiments of such clamping mechanisms. It has been discovered that large clamping surfaces and greater consistently applied clamping force is of use when dealing with heavy wirelines. Such wirelines are used in deep holes and for some drilling situations where higher gauge wirelines are employed.
While various devices have been employed for protecting an electrical wireline during a drilling operation, these devices are neither capable of, nor were they developed for the purpose of, resolving the above-described problems. Typical of the devices that have been used in drilling operations are those shown by the following U.S. Pat. Nos. 2,829,190 to Comlossy and 3,048,358 to Raulins. The patents to Comlossy and Raulins both illustrate protective members that are attached to the drill string. The wireline is arranged within a protector member and extends along the outer length of the drill string to the area of the drill bit. These devices are primarily designed to prevent the electrical wire from becoming twisted or wrapped around the drill string member as it is rotated and also to protect the wireline from being damaged by the drill string members within the hole being drilled. With the utilization of the side entry subassembly, however, the electrical wireline passes through the center of the drill string members and hence the clamps disclosed by the patents to Comlossy and McCarthy are not needed.
When drilling under certain conditions, it is necessary to insulate the electrical wire from certain conditions that might occur during the drilling operation. For this purpose, U.S. Pat. No. 3,835,929 to Suman discloses encasing the electrical wireline within a special conduit that extends from the top of the hole being drilled down to the drilling bit along the outside of the drill string assembly. Once again the types of problems that this patent seeks to avoid are largely solved by the use of the side entry subassembly thereby rendering the use of the insulating tubing unnecessary.
Various other devices have been known in the art for shielding a cable as it passes between two points. Such devices are illustrated in the following U.S. Pat. Nos. 2,258,745 to Dewey et al; 2,408,253 to Diebold; and 3,716,733 to Keith et al. These devices, however, are not utilized in downhole drilling operations.